Semiconductor die are commonly soldered or otherwise secured to the conductive pads of a substrate. One typical substrate is an insulated metal substrate (IMS).
Thus, IMS substrates are well known for mounting electronic components and insulating them from the substrate on which the devices are mounted. IMS reduces thermal impedance and conducts heat more efficiently than conventional printed circuit boards. While the invention is described herein as applied to an IMS substrate, it will be understood that the invention applies to a novel process of securing semiconductor die to the die pads of any type of substrate including direct-bond copper (DBC), FR4 and the like.
FIG. 2 shows a cross section of a conventional IMS structure. The conventional IMS structure includes a dielectric layer 14, which is usually a polymer sandwiched between copper circuit layer 12 and aluminum base layer 16. The circuit layer 12 will be patterned by conventional processes to provide pads for die mounting and related traces which form wiring interconnects between die. The dielectric layer 14 may be any conventional dielectric material that bonds to layers 12 and 14, and is thin and thermally conductive. Once the pads for die mounting are defined on the circuit layer, semiconductor die are to be soldered thereto.
Automated placement and soldering of the die is performed by placing the die with conventional pick and place tools together with solder wafers, and by a process of solder reflow to bond the die to the mounting pads defined in the circuit layer 12. Thereafter, the die are wire bonded to one another and/or to conductive lands of the substrate on which other die are mounted.
It has been found that, during the conventional solder reflow process, the rectangular die rotate more or less about an axis perpendicular to their surfaces. With the die so misaligned, the die or wire used to bond the die are subject to damage during wire bonding. The die may be damaged due to the bonder head striking improperly positioned die. The wire may be damaged by the bonding tool and misplaced wire bond.
It would be very desirable to prevent such die rotation during the solder reflow operation to prevent such die and wire damage during wire bonding.